The Battery Widget was introduced in Galaxy S23. You can use the battery widget to quickly check the battery levels of connected Bluetooth devices.
With the One UI 5.1 update, Samsung added the battery widget to Galaxy S22, S21, and S20. It works identically on all these devices.
This Galaxy S23 new features guide explains what the battery widget is, how to add the battery widget to the Home screen of Galaxy S23, S22, and S20, and how to use and manage this widget.